Qiubo Zhang/Lawrence Berkeley National Laboratory
At left, a red arrow tracks an individual copper atom's motion during an electrochemical reaction. At right, yellow arrows point to pits left behind in the catalyst surface.
Key takeaways
- Chemical reactions spurred with electricity are behind products essential for everyday life, and are expected to play a part in creating sustainable fuels derived from carbon dioxide.
- A newly developed technology for viewing electrochemical reactions at the atomic level enabled researchers led by UCLA and Lawrence Berkeley National Laboratory to watch a catalyst during an electrochemical reaction for the first time.
- They found that the orderly structure at the surface of the copper catalyst briefly turned into an amorphous mass.
All around us are products that depend on chemical reactions aided by electricity.
These electrochemical reactions are involved in manufacturing everything from aluminum and PVC pipe to soap and paper. They happen inside the batteries powering electronics, automobiles, pacemakers and more. And they may hold the key to sustainable production of energy and other resources that society relies upon.
Catalysts such as copper help drive reactions, so they're used in the vast majority of industrial applications for electrochemistry. Efforts to develop better catalysts have been hampered because what happens to these catalysts during reactions is poorly understood. Up till now, atomic imaging of catalysts could only happen before and after reactions, leaving researchers to figure out what occurred in between.
That limitation has fallen away thanks to a collaboration between the California NanoSystems Institute at UCLA and Lawrence Berkeley National Laboratory. In a new study published in the journal Nature, the team used a specially designed electrochemical cell to view the atomic details of a copper catalyst during a reaction that breaks down carbon dioxide — a potential route to recycle the greenhouse gas into fuel or other useful substances. The scientists documented liquid-like masses of copper appearing and disappearing at the catalyst surface, leaving it pitted.
"For something that is all over our lives, we actually understand very little about how catalysts work in real time," said co-author Pri Narang, a professor of physical sciences in UCLA College and a CNSI member. "We now have the ability to look at what's happening at an atomic level and understand it from a theoretical standpoint.
"Everyone would benefit from turning carbon dioxide straight to fuel, but how do we do it, and do it cheaply, reliably and at scale?" added Narang, who also holds an appointment in electrical and computer engineering at the UCLA Samueli School of Engineering. "This is the type of fundamental science that should move the needle in addressing those challenges."
Beyond the implications for sustainability research, these findings — and the technology that makes them possible — could advance the efficiency of electrochemical processes for numerous applications that impact everyday life. The study could help scientists and engineers move toward rational catalyst design instead of trial and error, according to co-author Yu Huang, Traugott and Dorothea Frederking Endowed Professor and chair of the materials science and engineering department at UCLA Samueli.
"Any information we can get about what really happens in electrocatalysis is a tremendous help in our fundamental understanding and search for practical designs," said Huang, who is a member of the CNSI. "Without that information, it's as if we're throwing darts blindfolded, and hoping that we hit somewhere close to the target."
Images were captured at Berkeley Lab's Molecular Foundry with a high-power electron microscope. This type of microscope uses a beam of electrons to see inside samples at a level of detail smaller than the length of a light wave.
Electron microscopy has run into obstacles revealing the atomic structure of materials working in liquids — such as the briny electrolyte bath needed for an electrochemical reaction. Running electricity through a sample adds a further degree of difficulty. Corresponding author Haimei Zheng, a senior scientist at Berkeley Lab and adjunct professor at UC Berkeley, and her colleagues created a hermetically sealed device that overcomes these hurdles.
The researchers conducted experiments to eliminate the chance that the electricity running through the system was affecting the resulting image. Zeroing in on the spot where the copper catalyst met the liquid electrolyte, the team captured changes that played out over about four seconds.
During the reaction, the structure of the copper shifted from an orderly crystal lattice, typically seen in metals, into an amorphous mass. That disordered bundle, containing atoms and positively charged ions of copper plus a few molecules of water, then flowed over the catalyst surface. As it did so, atoms exchanged between the ordered and disordered copper, leaving the catalyst surface pitted. Finally, the amorphous mass disappeared.
"We never expected the surface to turn amorphous and then return back to the crystalline structure," said co-author Yang Liu, a UCLA graduate student in Huang's research group. "Without this special tool for watching the system in operation, we would never be able to capture that moment. The advancement of characterization tools like this enables new fundamental discoveries, helping us understand how materials work under realistic conditions."
The study's co-first authors are Qiubo Zhang and Xianhu Sun of Berkeley Lab and Zhigang Song, a member of Narang's research group who is based at Harvard University. Other co-authors at Berkeley Lab are Sophia Betzler, Qi Zheng, Junyi Shangguan, Karen Bustillo and Peter Ercius, as well as Jiawei Wan, who is also affiliated with UC Berkeley.
The Department of Energy provided funding for this study, as well as for the Molecular Foundry at Berkeley Lab.
